This application is based on Finnish Patent Application No. 964065, filed in Finland on Oct. 10, 1996, the content of which is incorporated hereinto by reference.
The invention relates to an ATM telecommunication switch for switching telecommunication connections, said telecommunication switch comprising incoming lines, outgoing lines, and a switching field for switching any connection from an incoming line to a desired outgoing line, said switching field comprising inputs for supplying connections to said switching field, and outputs for supplying connections out of said switching field.
ATM telecommunication switches typically employ ATM switching fields (ATM=Asynchronous Transfer Mode). In these fields, ATM cells, or packets containing data, are switched from one connection to another in such a way that the connections remain unbroken, extending from an originator to a desired receiver. A characteristic of the switching fields is that they are susceptible to faults; a fault may affect either the entire switching field or only a part of it. A conventional and natural way of improving the reliability of ATM telecommunication switches is to duplicate the switching field of the switch. ATM switching fields are, however, expensive, wherefore it is extremely expensive to ensure their reliability by duplication. In addition, the aim is that all the connections switched through the switching field, e.g. virtual connections, have the same probability of succeeding. It is thus necessary to duplicate the entire switching field for reasons of reliability. The switching field is an essential part of an ATM telecommunication system, and the succeeding probability of the switchings performed in it, i.e. the service level, is to be kept even for all connections to be switched. It is obvious, however, that there may be connections with a lower service level and connections with a higher service level, i.e. connections based on duplicated switching, but this results in different service classes for connections. Usually a fault affects only one line of the switching field, and not the entire field. It is therefore useful to implement an ATM telecommunication switch in such a way that a fault occurring in a certain part, e.g. in one or more lines, of a switching field does not prevent the entire switch from operating.
An object of the present invention is to provide a solution to the problem with the prior art, i.e. how to cope with a fault occurring in an ATM switching field, particularly in a part of it. The object is to provide an ATM telecommunication switch and a method for using it in such a way that a fault occurring in a certain part of the switching field does not prevent the entire switch from operating.
This new type of ATM telecommunication switch is characterized by comprising a pre-selector provided between said incoming lines and said inputs for connecting a desired incoming line of said telecommunication switch to a desired input of the switching field.
The invention further relates to a method for switching telecommunication connections in an ATM switch comprising incoming lines, outgoing lines, and a switching field for switching any connection from an incoming line to a desired outgoing line, said switching field comprising inputs for supplying connections to said switching field, and outputs for supplying connections out of said switching field.
The method of the invention is characterized by providing said telecommunication switch with a pre-selector between said incoming lines and said inputs for switching a desired incoming line of said telecommunication switch to a desired input of the switching field.
The invention is based on the idea that an ATM switch is provided either with a pre-selector before or after the switching field or with a post-selector after the switching field. A pre-selector allows a desired incoming line of the switch to be connected to the desired input of the switching field. Correspondingly, a post-selector allows a desired output of the switching field to be connected to the desired outgoing line. A pre-selector preferably comprises at least one input connected to the incoming line of the entire switch, and a plurality of outputs connected to the inputs of the switching field. By means of these inputs, the line to be connected by the pre-selector can be guided to an operational input of the switching field. It should be noted that the term xe2x80x98pre-selectorxe2x80x99 is used herein to refer mainly to a pre-selector or a post-selector provided after the switching field.
Another feature of the invention is that the interfaces between the pre-selector and the ATM switching field comprise at least two interfaces towards the field per each incoming line of the pre-selector in the telecommunication switch.
An advantage of the ATM telecommunication switch and the corresponding method of the invention is that they render it unnecessary to duplicate the switching field of an ATM telecommunication switch; sufficient reliability of the switching field is ensured by the use of a pre-selector of the invention. This saves costs essentially, for it is very expensive to duplicate the entire switching field.